1. Field of the Invention
The present invention relates to transmission apparatus carrying out polar modulation so as to generate a vector modulation wave. More particularly, the present invention relates to transmission apparatus synthesizing an amplitude component modulation signal and phase modulation wave so as to generate a vector modulation wave, and communication apparatus and mobile wireless apparatus mounted with this transmission apparatus.
2. Description of the Related Art
Normally, a power amplifier provided at an output section of transmission apparatus in a wireless communication system requires both low distortion and high efficiency. Power amplifiers serving this kind of use are classified into amplifiers using transistors as a current source or using transistors as switches. Amplifiers using transistors as a current source may be class A amplifiers, class AB amplifiers, class B amplifiers and class C amplifiers. Further, amplifiers using transistors as a switch may be class D amplifiers, class E amplifiers and class F amplifiers.
Conventionally, class A or class AB linear amplifiers are used in order to amplify envelope fluctuation components in a linear manner, as high-frequency power amplifiers amplifying modulation waves containing envelope fluctuation components. However, there is the drawback that the power efficiency of linear amplifiers is inferior compared to non-linear amplifiers such as C class to E class amplifiers. Because of this, in the event that a conventional linear amplifier is used as a mobile type wireless apparatus such as a mobile telephone or mobile information terminal using a battery as a power source, because a class A or class AB linear amplifier of large power consumption is used, there is the drawback that usage time is short. Further, in the event that a conventional linear amplifier is used as base station apparatus for a mobile communication system installed with a plurality of large power transmission apparatus, there is the drawback of inviting increase in size of the transmission apparatus and increased heat generation.
Here, transmission apparatus having a highly efficient transmission function, equipped with an amplitude phase component extraction section, amplitude signal processing section, phase modulating section, and non-linear amplifying section etc. and carrying out polar modulation are well-known. EER (Envelope Elimination and Restoration) transmission apparatus configured so that a signal of a constant envelope level is received at a non-linear amplifying section that employs a non-linear amplifier of superior efficiency as a high-frequency amplifier, is proposed as this kind of transmission apparatus. Further, apparatus where non-linearity of an envelope signal for a non-linear amplifier is corrected using negative feedback so as to suppress amplitude distortion (Peter B. Kenington, “IGH-LINEARITY RF AMPLIFIER DESIGN,” volume 1, ARTECH HOUSE, INC., 2000, p. 426-443) are well known as transmission apparatus.
FIG. 1 is a block diagram showing an example configuration of conventional EER transmission apparatus. This EER transmission apparatus employs a configuration comprised of transmission data signal input terminal 11, amplitude phase component extraction section 12, amplitude signal processing section 13, phase modulating section 14, non-linear amplifying section 15 and transmission output terminal 16. In FIG. 1, transmission data signal Si(t) inputted by transmission data signal input terminal 11 is defined by the following equation (1):Si(t)=a(t)×exp[j×φ(t)]  (1)
Here, a(t) is an amplitude component modulation signal and φ(t) is a phase component modulation signal.
When transmission data signal Si(t) is defined as described in above equation (1), amplitude component modulation signal a(t) and phase component modulation signal φ(t) are extracted from transmission data signal Si(t) by amplitude phase component extraction section 12. The power supply voltage value of non-linear amplifying section 15 is then set via amplitude signal processing section 13 by this amplitude component modulation signal a(t). On the other hand, a phase modulation wave Sc(t) that is a carrier wave having an angular frequency ωc phase-modulated by phase modulating section 14 using a phase component modulation signal φ(t), is generated and inputted to non-linear amplifying section 15. The phase modulation wave Sc(t) at this time is expressed by the following equation (2):Sc(t)=exp[ωc×t+φ(t)]  (2)
At the output of non-linear amplifying section 15, a signal that is power supply voltage a(t) of non-linear amplifying section 15 and a phase modulation wave Sc(t) that is an output signal of phase modulating section 804 multiplied together, is amplified by a gain G of non-linear amplifying section 15, and outputted as an RF (Radio Frequency) vector modulation wave Srf(t). Vector modulation wave Srf(t) at this time is expressed by the following equation (3):
                                                                        Srf                ⁡                                  (                  t                  )                                            =                              G                ×                                  a                  ⁡                                      (                    t                    )                                                  ×                                  Sc                  ⁡                                      (                    t                    )                                                                                                                          =                              G                ×                                  a                  ⁡                                      (                    t                    )                                                  ×                                  exp                  ⁡                                      [                                                                  ω                        ⁢                                                                                                  ⁢                                                  c                          ⨯                          t                                                                    +                                              φ                        ⁡                                                  (                          t                          )                                                                                      ]                                                                                                          (        3        )            
As shown above, phase modulation wave Sc(t) inputted to non-linear amplifying section 15 is a phase modulation wave that is a modulation wave of a constant envelope level. It is therefore possible to use a non-linear amplifier of superior efficiency as a high-frequency amplifier, and, as a result, bring about a highly efficient and low distortion transmission apparatus. However, with the transmission apparatus shown in FIG. 1, in the event that there is a difference in delay time in the paths taken by the amplitude component and the phase component to reach non-linear amplifying section 15, distortion occurs in the vector modulation wave Srf(t) that is an output signal of non-linear amplifying section 15. For example, the signal transmitting the amplitude component is amplitude component modulation signal a(t) and the signal transmitting the phase component is phase component modulation signal φ(t) or phase modulation wave Sc(t), and there is a problem that delay times occur in the paths these signals are transmitted on.
FIG. 2 is a characteristic diagram showing the relationship between the frequency and amplitude of a vector modulation wave of the transmission apparatus shown in FIG. 1, with FIG. 2A showing the case where there is no difference in delay time, and FIG. 2B showing the case where there is a difference in delay time. Namely, FIG. 2 is a graph showing a frequency spectrum for vector frequency Srf(t) that is an output signal of non-linear amplifying section 15 of the transmission apparatus of FIG. 1. If there is a difference in delay time in the paths the amplitude component and phase component take to reach non-linear amplifying section 15, as shown in FIG. 2A, broadening of the frequency spectrum cannot be seen. However, when there is a difference in delay time in the paths the amplitude component and phase component reach the non-linear amplifying section 15 by, as shown in FIG. 2B, distortion of the vector modulation wave Srf(t) shown in FIG. 2B can be observed as broadening of the frequency spectrum. In a frequency division multiplex communication system where a plurality of channels are arranged on a frequency axis, this kind of broadening of the frequency spectrum causes interference with neighboring channels and therefore is not desirable.
Technology for removing distortion of vector modulation wave Srf(t) has therefore been proposed (for example, refer to Patent Document 1 (U.S. Pat. No. 6,366,177B1)). FIG. 3 is a block diagram showing a configuration for Conventional EER transmission apparatus such as Japanese Patent Document 1 etc. for improving distortion of vector modulation waves. Namely, FIG. 3 is a block diagram showing a configuration for transmission apparatus equipped with a function for correcting a difference in delay time occurring in paths the amplitude component and phase component take to reach non-linear power amplifying section 28. This transmission apparatus is comprised of transmission data input terminal 21, polar coordinate component modulation signal generating section 22 forming a modulation signal of an amplitude component and a phase component, timing correcting section 23, band-limiting filters 24 and 25, amplitude controlling section 26, phase modulating section 27, power amplifying section 28, transmission output terminal 29, phase angle measuring section 30, amplitude measuring section 31, and correction data storing section 32.
Next, a description is given of the operation of the transmission apparatus shown in FIG. 3. In addition to the same operation as the transmission apparatus shown in FIG. 1, this transmission apparatus selects correction data according to results of referring to an amplitude component and phase component of vector modulation wave Srf(t) that is the output signal of power amplifying section 28, and corrects and controls amplitude controlling section 26 and phase modulating section 27. Namely, the difference in delay time between the amplitude component and the phase component is known by again extracting and referring to the amplitude component and the phase component from the vector modulation wave Srf(t) and subjecting amplitude controlling section 26 and phase modulating section 27 to control corresponding to the correction of this difference. Further, timing correcting section 23 performs correction and control, and it is possible to directly adjust the time relationship between the amplitude component modulation signal a(t) and the phase component modulation signal φ(t).
From the above kind of correction control, adjustment is performed so as to cancel out differences between delay time occurring in paths the amplitude component and phase component take to reach power amplifying section 28 and distortion of the vector modulation wave Srf(t) that is the output of power amplifying section 28 can be achieved.
However, at the conventional transmission apparatus shown in FIG. 3, a difference in measured processing time occurs due to the respective functions between phase angle measuring section 30 and amplitude measuring section 31 being fundamentally different. As a result, the drawback occurs that it is not possible to measure the delay time between the amplitude component and the phase component in a precise manner.
It is necessary for phase angle measuring section 30 to function as a frequency discriminator that is a demodulator for a PM (Phase Modulation) modulation wave and an FM (Frequency Modulation) wave and is comprised of, for example, a pulse count detector circuit and a low pass filter circuit etc. With regards to this, it is necessary for amplitude measuring section 31 to function as an envelope detector that is a demodulator for AM (Amplitude Modulation) modulation waves and is comprised of, for example, a diode detector circuit and a low pass filter circuit, etc. Because of this, differences occur in measurement processing time due to differences in the circuit configuration of both circuits and it is therefore not possible to measure delay time in a precise manner.
In this manner, measurement processing time differences caused by differences in circuit configuration and differences in required performance etc. occur between phase angle measuring section 30 and amplitude measuring section 31. It is therefore not possible to accurately measure differences in delay time between the amplitude component and the phase component. Because of this, it is difficult to reduce distortion of vector modulation wave Srf(t) that is the output of power amplifying section 28 to a sufficiently small level.